1. Field of the Invention
The present invention relates to an intake port structure in an internal combustion engine, including: a combustion chamber, an intake port and an exhaust port which are formed in a cylinder head coupled to a deck surface of a cylinder block, an intake valve seat mounted between the intake port and the combustion chamber and opened and closed by an intake valve, and an exhaust valve seat mounted between the exhaust port and the combustion chamber and opened and closed by an exhaust valve.
2. Description of the Prior Art
If a swirl is generated in an air-fuel mixture drawn into the combustion chamber, the upper limit of engine speed with a lean burn of the air-fuel mixture is extended to improve the specific fuel consumption. The swirls include a lateral swirl and a vertical swirl. The lateral swirl is a flow of the air-fuel mixture drawn into the combustion chamber, which whirls about the axis of the cylinder. The vertical swirl is a flow of the air-fuel mixture drawn into the combustion chamber, which whirls along the wall surface of the combustion chamber, the wall surface of the cylinder and the top surface of the piston.
An intake port structure in which the wall surface of the combustion chamber connected to the intake valve seat for the intake valve is formed into a conical shape in order to generate such a vertical swirl, is conventionally known from Japanese patent Application Laid-open No. 248616/90.
In the above prior art structure, it is possible to generate the vertical swirl in the air-fuel mixture, but there is a problem that the amount of air-fuel mixture drawn is insufficient and as a result, a sufficient output is not obtained.